1. Field of the Invention
This invention relates generally to implantable medical devices for stimulating target tissue, and more particularly to, implantable pulse generators connecting to one or more elongated, electrode bearing leads and incorporating a locking mechanism for retaining a proximal end of the said lead in electrical and mechanical engagement with the input/output contacts of the pulse generator.
2. Discussion of the Prior Art
Dating back to the late 1950's and early 1960's, advances have been made in the treatment of patients through the application of electrical stimulation to target tissue from a pulse generator that is surgically implanted, subcutaneously or submuscularly, within a patient. A medical lead, comprising an elongated, flexible, insulating lead body and having surface electrodes thereon at a distal end and flexible conductors extending through the lead body for connecting the electrodes to a proximal terminal, is used to deliver electrical stimulation from the device to tissue abutting the electrodes and, in the case of cardiac rhythm management devices, to convey depolarization signals picked up by the electrodes back to the pulse generator.
In a typical prior art design, the proximal terminal of the medical lead comprises a rigid, straight pin having one or more electrical contacts disposed along its length. The pulse generator, in turn, has a molded plastic or epoxy connecter affixed to a hermetically sealed housing containing a battery power supply and electronic circuitry for delivering pulses in accordance with control signals provided by a microprocessor-based controller. The input and output nodes of the electronic circuitry are connected by feed-through wires that pass through suitable seals and connect to contact rings in a terminal receiving bore formed in the connector. The contact rings in the connector are adapted to mate with the electrical contacts of the lead terminal when the lead terminal is properly inserted and locked in place in the connector.
In the beginning, the implantable pulse generators were generally the size of a hockey puck. With improvements in circuit design and integrated circuitry, cardiac pacemakers and spinal cord stimulators are presently about the size of a silver dollar and about four times as thick. Efforts are still underway to further reduce the size and thickness of the implantable devices to render them less noticeable cosmetically. One design feature that has made it difficult to reduce the thickness dimension of such devices is the lead securing mechanism used in the header of the pulse generator.
In a typical prior art design, the lead locking mechanism comprises a block or blocks of metal disposed in the connector and having a longitudinal bore(s) for receiving the proximal end portion of the lead's proximal terminal therein. A threaded, transversely-extending bore that intersects with the longitudinal bore is also provided in the block for receiving a set screw. Once the proximal lead terminal is inserted into the longitudinal bore of the block comprising the locking mechanism, the setscrew is tightened down against the terminal in one or more locations. This forces the terminal pin into intimate contact with the wall of the longitudinal bore. Such a locking device mandates a connector whose thickness must be sufficient to contain the block of the locking member, the setscrew and a seal plug assembly used to prevent ingress of bodily fluids through the threaded bore. Such a construction typically drives a connector thickness of at least 7 mm. The prior art design also requires the use of a torquing tool to advance the setscrew.
It is also advantageous that one be able to replace a pulse generator without also having to replace the medical lead. Industry standards have been established for lead terminals in terms of their size (diameter and length), the location of contacts and location of insulation and seals. Therefore, any lead locking mechanism in a pulse generator should be such that it cooperates with a portion of the terminal that is in compliance with the standard, such as the proximal tip portion of the lead.
The present invention offers a lead lock mechanism that allows for a thinner connector than has heretofore been possible to achieve using setscrew technology. Moreover, the lead lock mechanism of the present invention does not require any special tools to effect locking. Also, the lead lock mechanism of the present invention is designed to accommodate any medical leads conforming to a given international standard.